The two pilots thought the overtaking operation would take place upstream of the Saint-Augustin Shoal, but they did not specify the place of overtaking. Furthermore, no information was exchanged concerning the special situation of the vessels and, accordingly, the pilots developed a false sense of security, relying on a brief exchange of information between the vessels and with MCTS. Thus, when the LT ARGOSY was observed overtaking the G.ORDZHONIKIDZE faster than expected, the two vessels were not manoeuvred to prevent the overtaking from happening in the channel of the Saint-Augustin Shoal. If the information concerning the special situation of the vessels had been broadcast over the MCTS radio telephone network when the vessels reported at the Saint-Nicolas calling-in point, it is reported that the overtaking manoeuvre would not have taken place abreast of the Saint-Augustin Shoal. The fact that this information was not broadcast by the vessel traffic regulator does not relieve the pilots of their responsibilities of ensuring a safe passage of the vessels of which they had the conduct. Although it is hard to foresee the onset and magnitude of the hydrodynamic interaction when overtaking in a restricted channel, it is incumbent upon navigators not to underestimate the effect of the hydrodynamic forces that reduce the directional control of a ship. The fact that both vessels had deep draughts and were making way parallel to the axis of a restricted channel indicates that the G.ORDZHONIKIDZE suffered the effect of hydrodynamic forces when it travelled along the north side of the channel. The loss of directional control contributed to the grounding.Analysis The two pilots thought the overtaking operation would take place upstream of the Saint-Augustin Shoal, but they did not specify the place of overtaking. Furthermore, no information was exchanged concerning the special situation of the vessels and, accordingly, the pilots developed a false sense of security, relying on a brief exchange of information between the vessels and with MCTS. Thus, when the LT ARGOSY was observed overtaking the G.ORDZHONIKIDZE faster than expected, the two vessels were not manoeuvred to prevent the overtaking from happening in the channel of the Saint-Augustin Shoal. If the information concerning the special situation of the vessels had been broadcast over the MCTS radio telephone network when the vessels reported at the Saint-Nicolas calling-in point, it is reported that the overtaking manoeuvre would not have taken place abreast of the Saint-Augustin Shoal. The fact that this information was not broadcast by the vessel traffic regulator does not relieve the pilots of their responsibilities of ensuring a safe passage of the vessels of which they had the conduct. Although it is hard to foresee the onset and magnitude of the hydrodynamic interaction when overtaking in a restricted channel, it is incumbent upon navigators not to underestimate the effect of the hydrodynamic forces that reduce the directional control of a ship. The fact that both vessels had deep draughts and were making way parallel to the axis of a restricted channel indicates that the G.ORDZHONIKIDZE suffered the effect of hydrodynamic forces when it travelled along the north side of the channel. The loss of directional control contributed to the grounding. The vessel traffic regulator did not broadcast over the MCTS radio telephone the information concerning the special deep-draught situation to which the two vessels were subject. Because they did not receive information from the MCTS and did not inform each other of their vessels' draughts, the pilots assumed that there was no special situation. The pilots intended to carry out the overtaking manoeuvre upstream of buoyQ22, but they did not confirm this verbally. The pilots did not manoeuvre the vessels to prevent an overtaking manoeuvre in the restricted channel of Saint-Augustin Shoal. By travelling together in the restricted channel, the two vessels suffered the effect of hydrodynamic forces. The effect of the hydrodynamic forces probably caused the G.ORDZHONIKIDZE to draw closer to the north side of the channel. The loss of directional control of the vessel probably contributed to the grounding.Findings The vessel traffic regulator did not broadcast over the MCTS radio telephone the information concerning the special deep-draught situation to which the two vessels were subject. Because they did not receive information from the MCTS and did not inform each other of their vessels' draughts, the pilots assumed that there was no special situation. The pilots intended to carry out the overtaking manoeuvre upstream of buoyQ22, but they did not confirm this verbally. The pilots did not manoeuvre the vessels to prevent an overtaking manoeuvre in the restricted channel of Saint-Augustin Shoal. By travelling together in the restricted channel, the two vessels suffered the effect of hydrodynamic forces. The effect of the hydrodynamic forces probably caused the G.ORDZHONIKIDZE to draw closer to the north side of the channel. The loss of directional control of the vessel probably contributed to the grounding. The G. ORDZHONIKIDZE probably grounded because it lost directional control when the hydrodynamic forces created between the G. ORDZHONIKIDZE and the LT ARGOSY moved it close to the north side of the channel. The regulator did not mention the special deep-draught situation of the two vessels on the MCTS radio telephone, and the pilots did not tell each other of this situation. Thus, they did not take it into account before planning the overtaking manoeuvre.Causes and Contributing Factors The G. ORDZHONIKIDZE probably grounded because it lost directional control when the hydrodynamic forces created between the G. ORDZHONIKIDZE and the LT ARGOSY moved it close to the north side of the channel. The regulator did not mention the special deep-draught situation of the two vessels on the MCTS radio telephone, and the pilots did not tell each other of this situation. Thus, they did not take it into account before planning the overtaking manoeuvre. Following this occurrence, a marine safety letter (MSI 01/97) was sent to Fisheries and Oceans to inform them that when information was exchanged between the Marine Communication and Traffic Services (MCTS) and the vessel pilots, the information about both vessels' deep draughts was not given to the pilots. The MCTS then reminded its personnel of the necessity of providing this information both to vessels performing overtaking manoeuvres and to vessels that are meeting each other. A reminder was also given to use the powers conferred under the Canada Shipping Act to ensure that the information is readily obtained, so that the alarm network is set off as soon as possible to inform the proper authorities.Safety Action Following this occurrence, a marine safety letter (MSI 01/97) was sent to Fisheries and Oceans to inform them that when information was exchanged between the Marine Communication and Traffic Services (MCTS) and the vessel pilots, the information about both vessels' deep draughts was not given to the pilots. The MCTS then reminded its personnel of the necessity of providing this information both to vessels performing overtaking manoeuvres and to vessels that are meeting each other. A reminder was also given to use the powers conferred under the Canada Shipping Act to ensure that the information is readily obtained, so that the alarm network is set off as soon as possible to inform the proper authorities.